Electrical switching arrangements

ABSTRACT

Various spark gap switches are disclosed in which an arc is caused to be struck, at a desired switching instant, between two electrodes. The electrodes are constructed so that a surface of one electrode faces an annular edge of the other, and a pronounced change in inter-electrode spacing occurs at this annular edge. The resultant magnetic forces produced at the annular edge when the arc is struck tend to hold the arc in a desired position. In some forms of the switches, the electrodes are generally planar. In others, one electrode is at least partially embraced by the other so as to define a semi-enclosed region within which the magnetic forces retain the arc.

United States Patent James 1 1 Se t. 4 1973 ELECTRICAL SWITCHING3,230,410 [/1966 Hafkemeyer et al. 313/217 ARRANGEMENTS [75] Inventor:Trevor Evans James, Abingdon, 'f Emmi'fer'eRoy Lake England Ass1stantExammer-Darw1n R. Hostetter Attorney-Larson, Taylor and Hinds [73]Assignee: United Kingdom Atomic Energy [57] ABSTRACT Various spark gapswitches are disclosed in which an arc is caused to be struck, at adesired switching instant, between two electrodes. The electrodes arecon- [3()] F i A li ti P i it D t structed so that a surface of oneelectrode faces an an- July 21 1970 Great Britain 35 388/70 edge thetheh and Pmhmmeed change inter-electrode spacing occurs at this annularedge. The [52] CL 313/325 313/217 resultant magnetic forces produced atthe annular edge 51 Int. Cl. 1101;" 17/04 when the are is etmek tendheld the are a desired [58] Field of Search 313 217, 325- ht seme fetmsef the switches, the eleetredee 315/36 are generally planar. In others,one electrode is at least partially embraced by the other so as todefine a semi- [56] References Cited enclosed region within which themagnetic forces re- UNITED STATES PATENTS the 2,290,526 7/1942 Berkey etal 313/217 6 Claims, 10 Drawing Figures PAIENIEn E sum 3 or 4 ELECTRICALSWITCHING ARRANGEMENTS BACKGROUND OF THE INVENTION The invention relatesto spark gap apparatus, and more particularly to spark gap switches inwhich an arc is struck, at a desired switching instant, between twoelectrodes.

BRIEF SUMMARY OF THE INVENTION According to the invention, there isprovided spark gap apparatus, comprising first and second electrodes inwhich a surface of the first electrode faces an annular edge on thesecond electrode which edge defines a pronounced change ininter-electrode spacing, and means for applying an electrical potentialdifference between the electrodes such that the magnetic forces actingon an are produced therebetween at the annular edge tend to limit thedirections of movement of the arc.

According to the invention, there is further provided spark gap switchapparatus, comprising first and second electrodes having a pronouncedand symmetrical change in spacing between them so as to define asemienclosed region between them, whereby magnetic forces acting on anarc set up between the electrodes tend to retain the are within the saidregion.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF PREFERRED EMBODIMENTSThe spark gap switches to be discussed are for switching high currentsfor long pulse times and, if required, with high accuracy of timing. Ineach case, a

gap is provided between two electrodes, and, in a manner to bedescribed, the current is caused to flow across the gap, at the instantrequired, in the form of an are.

In the spark gap switch of FIG. 1, two electrodes 8 and 10 are provided.Electrode 10 is in the form of a disc-shaped portion 10A and asupporting rod 108. The rod 108 is fixedly mounted relative to theelectrode 8 and separated therefrom by electrical insulation not shown.The spacing between the electrodes is non-uniform, such that the lengthof the gap 12 between them is less than the length of the gap 14 andpreferably greater than the length of the gap 16. In addition, theperipheral edge of the disc 10Ais' of reduced thickness to give anon-uniform electric field in the gap when a potential difference existsbetween the electrodes, the thickness of the edge being small comparedto the inter-electrode spacing.

In operation, a discharge between the electrode 8, 10 can be initiatedin one of a number of ways. For example, a high potential difference maysuddenly be applied between the electrodes 8 and 10. This high potentialcan be applied by suddenly raising one of the electrodes from zerovolts; instead a steady potential difference, not quite sufficient tobreak down the gap between the electrodes can be applied between them, avoltage pulse then being applied to one of the electrodes sufficient toraise the potential difference to the breakdown value. Alternatively, asteady potential difference, again not quite sufficient to causebreakdown, can be applied between the electrodes and then the spacing orgas pressure between the electrodes can be suddenly reduced to causebreakdown to occur, or the actual gas can be changed from one having arelatively good resistance to electrical breakdown to one having arelatively poorer resistance to electrical breakdown (e.g. fromcompressed air to argon or from SF, to air) so as to cause breakdown tooccur; these methods are not so satisfactory when very high timingaccuracy is required.

Whichever method is used, the intense non-uniform electric field set upat the edge of the disc 10A causes breakdown to occur across the gap 12,so that an arc is struck here. The resultant magnetic force produced bythe arc and the electrode currents is such that, provided the arccurrent and the lengths of time for which it is maintained aresufficient, the arc is caused to shift around the peripheral edge of thedisc 10A until it reaches the gap 14, this being the position of maximuminductance, that is, maximum arc length. Ifthe are current and/or itstime of existence is not sufi'icient to cause the arc to move round tothe gap 14, it will remain in the gap 12. In either case, however, itwill not move to or through the narrow gap 16.

Thus, the arc is held in a confined position remote from the electricalinsulation separating electrodes, and the damage to the insulation bythe arc will thus be minimised. Furthermore, the position in which thearc is initially maintained traps erosion products within theinter-electrode space.

The shape of the disc 10A is such that erosion caused by the arcinitiation is spread round the periphery of the disc 10A. The life ofthe electrode 10 can therefore be made as long as necessary by choosinga sufficiently large diameter for the disc 10A. Erosion of the disc 10Amerely reduces the diameter of the disc while maintaining approximatelythe same gap dimensions, and the life of the electrode 8 is alsoprolonged. Thus, triggering perfonnance, voltage hold-off, and arevoltage will not vary as a result of erosion until the disc diameterbecomes very small. These factors combine to increase the life of theswitch.

The spark gap switch FIGS. 2A to 2D is generally similar to that of FIG.1, and similar parts are similarly referenced; as shown, the disc 10A ofFIGS. 2A to 2D arrangement has a fatter cross-section than that inFIG. 1. FIG. 2A shows one method by which an are discharge can beinitiated. Here, anadditional electrode 18, which is electricallyinsulated by insulation 20 from the electrode 8, is used. A potentialdifference (which may be zero), insufficient to cause breakdown, isapplied between the electrode 8 and 10. At the desired switchinginstant, a potential is suddenly applied to electrode 18, and causesbreakdown to occur initially either between electrode 18 and electrode10 or between 18 and electrode 8 and subsequently between the electrode8 and 10.

FIG. 2B shows a modification in which two or more auxiliary electrodes18 are provided. This may be advantageous in that it prolongs the lifeof disc A and the electrode 18 by initiating breakdown at more than onepoint around the periphery of the disc. Instead of the two electrodes 18in FIG.2B being separate, they may be in the form of a single annularring electrode which physically divides electrode 8 into two parts 8Aand 8B.

FIG. 2C shows another variant. Again, a potential difference (which maybe zero) insufficient to cause breakdown is applied between electrodes 8and 10. At the desired switching instant, a plasma jet is injectedthrough an orifice 22, and breaks down the gap 14 causing an arc to beestablished between electrodes 8 and 10. More than one orifice 22 may beprovided and this may be advantageous in that breakdown can be initiatedat a number of points around the disc 10A thus prolonging electrodelife.

FIG. 2D illustrates a further way in which an arc can be struck. If theorifice 22 is made annular in form, the electrode 8 is separated intotwo electrically isolated electrodes 8A and 88. An arc can thus bestruck between these two electrodes across the gap provided by theorifice. This is achieved by connecting a capacitor of the requiredenergy between parts 8A and 8B, and applying a voltage pulse to eitherelectrode 8A or 8B. The resultant magnetic force on the auxiliary arcmoves it towards disc 10A so that if a potential difference is appliedbetween electrodes 8 and 10, breakdown will occur across gap 14. Toensure that the auxiliary arc is initiated at gap 23 after erosion hastaken place, it may be advantageous to have a disc-shaped outer edge toeither electrode 8A or 88 at gap 23 as shown or place an insulator 24between parts 8A and 8B, or both the disc-shaped edge and the insulatorcan be used together. Alternatively, an auxiliary annular electrodeplaced between electrodes 8A and 88, as for example shown in FIG. 28 byelectrode 18, will ensure that the auxiliary arc is struck across gap23. In this case, breakdown is initiated between electrode 8A and 88 byapplying a voltage pulse to electrode 18.

FIGS. 3A and 3B show two variants of a further spark gap switch, andagain parts similar to those in FIG. 1

are similarly referenced. In the variant of FIG. 3A, the

electrode 10 does not have a disc-shaped portion but is cup-shaped witha hole 28 whose annular edge faces the electrode 8, which is in theformof a cylindrical solid, and produces a pronounced change ininterelectrode spacing. When an arc is struck at the gap 12, using oneof the methods previously described, the effect of the annular edge isto create magnetic forces which tend to drive the arc towards the centreof the hole; the arc is therefore prevented from damaging the insulation(not shown) separating the upper parts of the electrodes. Theconfiguration of the variant of FIG. 3A, however, is such that erosionproducts are not so well retained within the gap as in the embodimentsof FIGS. 2A and 2B.

In the variant of FIG. 3B, the two electrodes simply comprise twogenerally flat plates as shown with electrode 10 being provided with ahole 2% whose annular edge faces the electrode 8 across the gap 12 andhas the same effect as in FIG. 3A. Again, the arc is struck across thegap 8 at the desired switching instant, by any one of the methodsdescribed above, and the configuration retains the arc at the centre ofthe spacing. Here,

the erosion products are also more or less retained within the spacing.

In FIGS. 3A and 3B, the holes 28 can be replaced by circular recessesfacing the lower ends of the electrodes 8.

The embodiment of FIG. 38 can be modified by inserting a rod upwardlythrough the hole 28 to provide electrical connection to the electrode 8.In a further modification, a plurality of holes 28 can be formed in theelectrode 10, each such hole facing the electrode 8. Each such hole canhave a rod through it.

In FIG. 4, the electrode portion 10A is of disc-like form with athickness less than the inter-electrode spacing, while the electrode 8is of planar form. As before, the arc is struck across theinter-electrode gap 12 by one of the methods described above, and thenonuniform field existing at the annular edge of priphery of the disc10A helps to give a rapid striking action and reduces erosion of the twoelectrodes. As shown, the electrode 8 is annular in form, and again themagnetic forces set up on the arc ensure that the end of the arc onelectrode 8 tends to move outwardly along electrode 8. The spacingbetween electrode 8 and disc portion 10A can be uniform or can increasein a radially outward direction.

FIGS. 5A and 58 respectively show variants of the further spark gapswitches of FIGS. 3A and 33; parts similar to those in FIGS. 3A and 3Bare similarly referenced. In the variant of FIG. 5A, the spacing betweenthe electrodes is uniform along the horizontal and is also uniform, butsmaller, along the vertical. At the desired switching instant, an arc isstruck at the gap 14 using one of the methods previously described.Because of the small size of the gap 116 as compared with the gaps l2and 14, the arc is prevented from moving to or through the gap 16; thearc is therefore prevented from damaging the insulation (not shown)separating the upper parts of the electrodes.

In the variant of FIG.5B, the horizontal spacing between the electrodes8 and H0 is not uniform. In this variant, the two electrodes may simplycomprise two generally flat plates as shown. Again the arc is struckacross the gaps 12 or 14, at the desired switching instant, by any oneof the methods described above, and

the configuration of the inter-electrode spacing retains the are at thecentre of the spacing. Here, the erosion products are also more or lessretained within the spacmg.

It will be appreciated that the semi-enclosed configuration shown inFIGS. 1 to 2D and 5A and 5B and in the versions of FIGS. 3A and 3B inwhich the holes 28 are replaced by recesses are advantageous over theopen forms of FIG. 4, in that they provide a predetermined maximumimpedance for the arc and lend themselves to operation under pressurizedconditions.

What is claimed is: ll. Spark gap switch apparatus, comprising a firstelectrode of a disc shape defining first and second opposed surfaces, asecond electrode including an annular surface de fining a hole therein.the first electrode being mounted with one of said surfaces facing andoverlapping the said annular surface and hole of the second electrodewith the periphery of said one surface defining a pronounced change ininter-electrode spacing, and

means for applying an electrical potential difference between theelectrodes to produce an arc therebetween, said means including aconductive rod connected to the first electrode and directed transversely of said one surface of the first electrode to pass through thehole in the second electrode with the current flow in the arc andelectrode surfaces producing magnetic forces acting on the are whichtend to keep the arc away from the said hole.

2. Apparatus according to claim 1, in which the sec ond electrode atleast partially embraces the first electrode.

3. Apparatus according to claim 2, in which the interelectrode gapincreases in a direction away from the periphery of the hole in thesecond electrode, so as to tend to move the are away from the rod.

4. Apparatus according to claim 1, in which the periphery of said firstelectrode has a thickness which is small compared to the inter-electrodegap.

5. Apparatus according to claim 1, including striking means for strikingthe said arc at a desired switching instant.

6. Spark gap switch apparatus, comprising a first disc-shaped electrode,

a second generally cup-shaped electrode, a curved upper end portion ofthe side wall of the cup extending transversely to the cup axis so as topartially close off and top of the cup and to define a hole throughwhich the said cup axis passes,

an electrically conductive rod attached to the first electrode andextending transversely to the surface thereof and supporting the firstelectrode inside the cup defined by the second electrode with a majorsurface of the disc-shaped first electrode overlapping the upper endportion of the second electrode and with the rod extending out throughthe said hole defined by the second electrode such that theinter-electrode gap increases towards the periphery of the firstelectrode, and

means for striking an are between the electrodes which produces magneticforces tending to retain the are inside the cup and away from the saidhole.

* 1F i I l

1. Spark gap switch apparatus, comprising a first electrode of a discshape defining first and second opposed surfaces, a second electrodeincluding an annular surface defining a hole therein. the firstelectrode being mounted with one of said surfaces facing and overlappingthe said annular surface and hole of the second electrode with theperiphery of said one surface defining a pronounced change ininter-electrode spacing, and means for applying an electrical potentialdifference between the electrodes to produce an arc therebetween, saidmeans including a conductive rod connected to the first electrode anddirected transversely of said one surface of the first electrode to passthrough the hole in the second electrode with the current flow in thearc and electrode surfaces producing magnetic forces acting on the arcwhich tend to keep the arc away from the said hole.
 2. Apparatusaccording to claim 1, in which the second electrode at least partiallyembraces the first electrode.
 3. Apparatus according to claim 2, inwhich the inter-electrode gap increases in a direction away from theperiphery of the hole in the second electrode, so as to tend to move thearc away from the rod.
 4. Apparatus according to claim 1, in which theperiphery of said first electrode has a thickness which is smallcompared to the inter-electrode gap.
 5. Apparatus according to claim 1,including striking means for striking the said arc at a desiredswitching instant.
 6. Spark gap switch apparatus, comprising a firstdisc-shaped electrode, a second generally cup-shaped electrode, a curvedupper end portion of the side wall of the cup extending transversely tothe cup axis so as to partially close off and top of the cup and todefine a hole through which the said cup axis passes, an electricallyconductive rod attached to the first electrode and extendingtransversely to the surface thereof and supporting the first electrOdeinside the cup defined by the second electrode with a major surface ofthe disc-shaped first electrode overlapping the upper end portion of thesecond electrode and with the rod extending out through the said holedefined by the second electrode such that the inter-electrode gapincreases towards the periphery of the first electrode, and means forstriking an arc between the electrodes which produces magnetic forcestending to retain the arc inside the cup and away from the said hole.